Hot Water Woes

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As I have been asked about my plumbing setup and how I choose to rectify the hot water lapse in the shower I will post it on here so that whomever might benefit from the info can. The problem being that when taking a shower "Navy Shower" and using the trickle switch on the shower head, this is supposed to allow the water to dribble so that the hot and cold water stay present at the head, however in an unbalanced system one will over power the other and when the valve is re-opened you will get too much hot or cold until the balance is restored. In our systems, keeping in mind that my trailer is #69 produced in early 2015, the configuration is such that the cold water has a more direct line to the shower head than the hot and with the 6 gallon tank the hot water would lose some of its pressure there too. So basically the system allows the cold to build more pressure at the shower head and over power the hot line (My system is dry right now or I would throw a pressure gauge on it to see the difference to be accurate). The easy fix for the problem is to insert a check valve into the hot water line between the hot water heater and shower head. This will not allow the cold water to over power the hot and push it back up its own line, placement isn't critical as the return flow is stopped the entire length in front of it. One thing to note is that the kitchen faucet tees off the hot water line under the front set of kitchen drawers, so behind that would allow reverse flow if the kitchen faucet is not closed completely.

One big thing to note is that this will effectively stop a gravity drain of the hot water line from the shower, however blowing out the line and filling with pink stuff would be unaffected.

I also did some checking on the initial flow of hot water with the Truma system as has been discussed recently. For those of you who are meticulous about your boondocking and water conservation, the initial flow of hot water to clear the cold out of the line results in a waste of .22 gallons, if not recaptured. For those with the suburban heater, creating a recirculation system is easily possible, however you would need to be comfortable removing the shelf unit in the bathroom to access the PEX as close to the faucet as possible to install a tee and return line, then determine where you would like an open/close valve and reconnect to the system in front of the pump. This way when you turn on the pump, it pressurizes the system and if you open THAT valve, only the hot water flows in a circle to clear the line of cold before the initial turn on.

I would imagine that Oliver would be able to add this configuration easily enough for a couple hundred dollars on any new trailer with a suburban to get the same effect.

The check valve that I used is the Shark Bite, I prefer these as they do not require any crimping and can be removed if draining the line is necessary.

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Being that both the hot and cold water are ran by the 1 pump, overpower wouldn't be an issue... At least I don't think :) I don't understand how hot water can be pushed anywhere other then out of the flex hose after the valves as is because the entire system is pressurized by the one pump, so it's going to be equal regardless of the pipes sizes. I don't see a way for the hot water being pushed backwards to happen, because it's running at the same pressure from the same pump. It would be nice if we could just set the hot water temp ourselves in a perfect world like I have done here at the house. I turn on the hot, take a shower and never need to add any cold unless it's the middle of summer and I want a cool shower. I sure wish the temps were adjustable in the rv water heaters... That would end this problem. Every place that I look to find a schematic for the Truma Basic or Comfort, it's always the same schematic that shows all 3 with the added fittings inside for the comfort+. It sure would be nice to be able to get the right interior schematic for our comfort model... Either way there is an upgrade that you can buy to turn either into the Comfort+, which is something that Oliver should offer along with the Comfort+ model also. All I really need to see is a pic of the left inside where the recirculation pump is, to see what's there inside the Comfort model but I can't find one anywhere online... I'm not trying to say that you did anything wrong, I'm just saying that I don't understand your way of fixing it . And respectfully, I think a different way then most people :) My wife has a different name for it :)

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It would be nice if we could just set the hot water temp ourselves in a perfect world like I have done here at the house.

And as I have done at my house, with a Takagi unit back before you could by the on demand system in the big box stores. This was what I checked for and ultimately why I decided the Truma system wasn't worth it to me.

While the second attachment you have is somewhat of a parts list, this one is more of an image, of the left side actually, maybe it will help your search. 18 is the circulation pump

1

Randy

One Life Live It Enjoyably

2017 F350 6.7L SRW CC LB

2015 Oliver Elite II Hull #69

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Nope, that's the Comfort+ schematic, same and only one that I could find. Is the same recirculation pump and fittings even in the comfort?... is my question... Because if it is, then a quick Tee and some line would turn it into the +, that's why I'm thinking the inside is different ant it may not need a recirculation pump for a short circle because the heat transfer would push it through like in the old wood fired Kitchen stoves with the water line plumbed in the back for the household hot water.

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I don’t see a way for the hot water being pushed backwards to happen, because it’s running at the same pressure from the same pump.

I will work from two trains of thought, but first let me state that I have no working or education background on this subject, I believe I read in one of your other posts you have a background in boilers, so mine is from what I see figuring out my problem and what I then find researching it out on the web to explain why.

1. If one pump feeds the system and one path is 1 foot and the other path is 10 feet where they rejoin, the "by whatever margin" the longer path would have lost more of its pressure just by the friction of passing through more pipe. The single pump trying to reach balance would therefore find it, in my mind anyways, at the 4.5 foot mark past the join point, which would then be center of the path.

2. Cold water has a higher density than hot water, thus if the pressure IS the same at that point would the higher density liquid be able to move the lower density liquid or if not move it then overwhelm it?

Now, in a closed system I would agree that when the two ends were joined that both sides would hold their own equally, but with the dribble valve engaged, this bleeds off pressure and is what allows the denser higher pressure fluid to attempt to equalize.

Otherwise, I do not have the education to understand the why, but stopping the reverse flow as described, corrected the problem for me and I'm just a get-r-done kind of guy, without a lot of education to get in my way.

1

Randy

One Life Live It Enjoyably

2017 F350 6.7L SRW CC LB

2015 Oliver Elite II Hull #69

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Sorry, I am almost always on my phone when on here and cheated the easy way for the screen capture.

Here is the link for the Truma PDF it says it's all three systems and just lists that connector 3 is for the plus. So basically the guts are the same just that tee is added, makes me think they are probably all able to have it internally, just whether it's hooked up and configured.

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I don’t see a way for the hot water being pushed backwards to happen, because it’s running at the same pressure from the same pump.

I will work from two trains of thought, but first let me state that I have no working or education background on this subject, I believe I read in one of your other posts you have a background in boilers, so mine is from what I see figuring out my problem and what I then find researching it out on the web to explain why. 1. If one pump feeds the system and one path is 1 foot and the other path is 10 feet where they rejoin, the “by whatever margin” the longer path would have lost more of its pressure just by the friction of passing through more pipe. The single pump trying to reach balance would therefore find it, in my mind anyways, at the 4.5 foot mark past the join point, which would then be center of the path. 2. Cold water has a higher density than hot water, thus if the pressure IS the same at that point would the higher density liquid be able to move the lower density liquid or if not move it then overwhelm it? Now, in a closed system I would agree that when the two ends were joined that both sides would hold their own equally, but with the dribble valve engaged, this bleeds off pressure and is what allows the denser higher pressure fluid to attempt to equalize. Otherwise, I do not have the education to understand the why, but stopping the reverse flow as described, corrected the problem for me and I’m just a get-r-done kind of guy, without a lot of education to get in my way.

I've hit Like on all of your posts at least 3 times, closed the page twice and still... lol I know it will come around :)

Here's my answers to what you wrote above -

1. If one pump feeds the system and one path is 1 foot and the other path is 10 feet where they rejoin, the “by whatever margin” the longer path would have lost more of its pressure just by the friction of passing through more pipe. ____ The cold water is denser but the hot water actually has more pressure behind it because the molecules are racing to create the heat. But what's happening also is that even though the the dribble valve is open, it's not running the hot water fast enough to keep the uninsulated line from cooling down between the valve and the water heater. Insulating all of the hot water line to the shower really makes a difference. Plus because the pressure will equalize between the valve and the dribbler, more cold will be coming into that line then before. A pressure regulator would slow it down but still, because the hot water is constantly cooling in the pex tubing, what we did in the Casita was to have a double handle shower or separate controls for each. I would then still dribble the hot but turn the cold off. I'm thinking about calling Little House Customs and adding the Shower Mod to our list of thing we are going to have them do on our way home. I really like having hot and cold water valves separate.

2. Cold water has a higher density than hot water - Yup but the warmer the water the more the pressure. So as the hot water cools down in the line it will constantly be trying to equalize as the molecules slow and the sitting warm water will condense while drawing more cold water in to mix with. So the check valve will work to a point and that's a good thing - because the cold water won't get past the check valve as the warm water condenses, so it will be forced to draw the extra needed hot water as it cools from the hot water tank instead. By putting in the check valve, it's allowing the hot water to cool more slowly without the influx of cold water at all. And they aren't fighting each other while drastically trying to equalize; now not only pressure wise but temperature wise, because the hot water will draw the cold water into itself as it condenses to try and stabilize the temperature.

Now just to add to your work load, try insulating the hot water line with the best and tightest fitting insulation that you can find. The insulation will only help keep the hot water warmer as it sits in the pipe for a short time, so it works for taking a shower because it will only be turned off for a few minutes but if you are washing dishes, then shut it off and come back half an hour later, the water will have already cooled back down inside the pipe. So there's no need to run insulation everywhere, just straight to the hot water valve :)

I read through the PDF and like you said, the only difference is the Tee. So I'm going to call Jason and see if they offer the Comfort+ with the return Line.

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Thank you for taking the time to explain it. I really do appreciate when people who have the knowledge are willing to take the time to impart it rather than just state "because that's how it works"

So basically, I got lucky, the system is small enough and the durations are short enough that in this situation the check valve works but in a larger scenario it wouldn't be as effective. As you explain it, the closer the check valve is to the faucet the greater the affect it will have then. Thanks for that clarification.

One of the nice things about the way Oliver laid out the system, at least around my hull number is that the water lines lay in the channel directly underneath the bathroom heat duct, so when the furnace runs it warms the water lines that run to the shower.

We have two showers at home, my wife prefers the aesthetics of the single mixer valve, so insisted on it for her remodel. For the other, I put in the single controls with a shut off, she now understands the benefits of the single system and prefers it too.

1

Randy

One Life Live It Enjoyably

2017 F350 6.7L SRW CC LB

2015 Oliver Elite II Hull #69

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I would think you might get the same pressure on both lines. Usually when you pressure a line, you have the same pressure throughout the length of a line. If you were to run a 200' air hose would the tire gauge read the same as the compressor at the hose end? What you would end up with is less volume. I would think you have a more direct flow on the cold side, and some restrictions on the hot side as the water is diverted through the heater where it is slowed somewhat to have it time to heat. Maybe a solution might be to have smaller diameter tubing placed the further down the line the flow goes. Same as is done in home plumbing. This is done so that if someone flushes in one part of the house you don't get scalded elsewhere. Just on the camper the line runs are so much shorter it would be hardly noticeable? (Just a thought-- not tested)

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It's not enough to say different pressures exist on the hot and cold lines. Not exactly. Static pressure with all faucets off will be identical on both hot and cold.

When showering, you are looking for a ratio of hot and cold that suits your temperature needs. This might be 70% hot and 30% cold, for instance. So you balance the restrictions at the shower faucet to achieve this ratio. You are measuring restrictions with a temperature gauge. You are the temperature gauge.

At that moment, all restrictions in both hot and cold lines are factored in. It's true that the hot may have more length and more fittings to get through on the way to the shower, but it doesn't matter. It's a dynamic system and it is in balance at the flow rate you want at that moment. For instance, it might be supplying 3 gallons per minute total at the shower head, with a ratio of 70% hot and 30% cold.

Now you slow the flow with your trickle valve and the restrictions all change. At 1/8 GPM, for instance, the flow restriction through the entire plumbing system changes and becomes more equal between hot and cold. The hot and cold line restrictions change unequally. The flow restrictions through the hot and cold valves changes significantly and the shower head restriction changes. So your ratio changes, due to several factors, causing your temperature to change. When you open the trickle valve to full flow again, the original restrictions return and the original temp returns, once the flex line is flushed out. A small difference will still be present from the heat loss through the uninsulated hot line that was flowing slower and losing more heat during trickle.

You would probably have better results by turning the flow off completely at the shower head, than reducing it to a trickle. That way all flow will be either at full volume or off. The valve restrictions and the entire hot and cold net restrictions will remain in balance to deliver the temp you want.

A check valve in the system, as you suggested, will do no good and reading the pressures on a gauge will be meaningless. Static pressure will always be equal with no flow. Gauge pressures near the shower faucet are meaningless because it's a flow ratio you are interested in and that flow is measured in temperature, not pressure.

I suppose you could try some kind of temperature controlled shower valve, but it won't be satisfactory. Just try a total shutoff at the shower head and put up with a small temperature fluctuation.

1

John

"I only exaggerate enough to compensate for being taken with a grain of salt."